Recording paper



March 3, 1959 H. l. CHAMBERS 2,376,060

RECORDING PAPER Filed Jan. 22, 1957 2 Sheets-Sheet 1 F/Gl.

Pl GME N 7' I3 P/GMEN T l3 1:76. 2. 2 CARBON l2? v v A IN VENTOR.HERBERT CHAMBERS A TTORNEVS March 3, 1959 H. l. CHAMBERS RECORDING PAPERFiled Jan. 22, 1957 2 Sheets-Sheet 2 WR/T/NG CURRENT GENERATOR RECORD/N6'AMPL/F/ER FIG. 4.

INVENTORL HERBERT CHAMBERS RECORDING PAPER Herbert I. Chambers,Pasadena, Calif., assignor to Consolidated Electrodynamics Corporation,Pasadena, Calif., a corporation of California Application January 22,1957, Serial No. 635,484

1 Claim. (Cl. 34674) This invention relates to coated recording paper,and more particularly, to electrosensitive paper which is used in directsimultaneous recording of a plurality of signals.

The paper of this invention is particularly suitable for recording theoutput of multi-channel string galvanometers.

In a typical string galvanometer, the writing element is a string, i.e., a movable conductor. The string is supported at its two ends so thatits central portion can be deflected transversely a relatively largedistance in a fixed plane to provide the large amplitudes of motionwhich are required for recording directly.

The conductive string is located in a magnetic field perpendicular tothe direction of the magnetic field, so that the string movestransversely with respect to the magnetic flux in accordance with themagnitude of the electric current which flows through the string inresponse to an applied signal. Preferably, the string is supported ateach end by springs so that as the string is deflected in eitherdirection, the springs permit the ends of the string to move closertogether.

For direct writing on electrosensitive recording paper, an anvil havingan edge located at the central portion of the string is employed toguide a strip of recording paper adjacent the center of the string. Theedge of the anvil is perpendicular to the string, and theelectrosensitive paper is moved over the edge ofthe anvil so that itpasses between the anvil and the string. Suitable means are provided forurging the string against the paper Where the paper passes over the edgeof the anvil, and a source of electrical writing voltage is appliedacross the paper and the string so that an electric current passesbetween the paper and the string at the intersection of the string andthe line formed where the recording paper passes over the edge of theanvil. The current density at the point of contact between the paper andthe string is sufiiciently high to visibly affect the paper at thatpoint. Thus, as the strip of paper is pulled over the edge of the anvil,a trace is formed on the paper which provides a record of thedeflections of the string in response to an applied signal.

In many types of measurements it is desirable to record the traces oftwo or more signals simultaneously on a common piece of electrosensitivedirect recording paper. In such cases, a multi-channel oscillograph isused. Such a device employs as many strings as necessary to record thevarious signals, each string being adapted to receive a respectivesignal. The strings are usually placed side by side, parallel and in acommon plane. Each string is adapted to travel over a separate givenwidth or channel of the paper in recording its respective measurement.

One of the difiiculties presented by multi-channel direct recordingoscillographs with presently available electrosensitive paper is that ofobtaining satisfactory traces when signals of different frequencies arerecorded simultaneously. A relatively high writing voltage is requiredfor satisfactory recording of a high frequency signal, because of therelatively high velocity of the string across the 2,876,060 PatentedMar. 3, 1959 surface of the paper. On the other hand, less writingvoltage is required for recording a low frequency signal because ofbetter contact between the paper and the slower moving string. Thepresently available electrosensitive direct recording paper has a commonelectroconductive surface, and the use of a writing voltage sufiicint torecord a high frequency trace in one channel sometimes burns the paperin another channel being used to record a lower frequency.

This invention overcomes this difiiculty by providing anelectrosensitive direct recording paper for multi-channel recording,which has a series of elongated and laterally spaced recording channelswhich are electrically insulated from each other. Thus, the properwriting voltage can be applied to each respective recording channel inaccordance with the frequency which is to be recorded on the particularchannel.

Briefly, the invention contemplates an electrosensitive recording paperfor multi-channel recording in which the paper comprises a base ofelectrically insulating material having elongated and laterally spacedlongitudinal strips of conductive material to establish laterally spacedconductive channels. Each conductive channel is electrically insulatedfrom adjacent channels and has a surface coating of such character to bevisibly altered by the application to it of an electrical markingcurrent.

In the presently preferred form of the invention, the strip ofconductive material is a layer of carbon applied to the surface of thebase material and is covered by the electrosensitive surface coating.

In an alternate form of the invention, the conductive strips are formedby impregnating laterally spaced channels of the base material with aconductive material such as carbon.

Electrosensitive direct recording paper is well known, and such paper isdescribed in U. S. Patents 2,554,017 and 2,555,321. However, as statedabove, all electro sensitive paper now available is made with a commonelectroconductive layer which covers the entire area of the paper, andtherefore is not suitable for multi-channel recording where differentwriting voltages are required for the various channels. This inventionprovides a plurality of insulated recording channels on a common sheetof electrosensitive direct recording paper on which a plurality oftraces can be recorded simultaneously, even though difierent writingvoltages are required for the various channels. The advantages ofmulti-channel recording on a single strip of paper are that a singleroll of paper is easy to handle and process, and the informationrecorded in each channel is automatically mounted on a common base sothat the output from the various channels may easily be visuallyinspected and compared with each other.

These and other aspects of the invention will be more fully understoodfrom the following detailed description taken in conjunction with theaccompanying drawings in which:

Fig. 1 is a fragmentary plan view of the presently preferred form ofmulti-channel direct recording paper according to the invention;

Fig. 2 is a view taken on line 22 of Fig. 1;

Fig. 3 is a schematic side elevation of a direct recording stringgalvanometer;

Fig. 4 is a perspective view of an anvil of a direct recording stringgalvanometer of the type shown in Fig. 2, the anvil being adapted foruse in a galvanometer in which two channels are recorded simultaneously;and

Fig. 5 is a transverse cross-sectional view of an alternate form of thepaper of this invention in which the conductive strip is embeddeddirectly in the base material of the paper.

Referring to Figs. 1 and 2, the direct recording paper includes anelongated base or carrier 10 which may be made of paper or othersuitable pliable material, such as fabric, photographic transparencies,or the like. A pair of elongated, longitudinal and laterally spacedrecording channels 11 are formed on one surface of the base of thecarrier. Each recording channel includes an elongated conductive layer12 of a suitable material, such as carbon, laid down on the surface ofthe carrier. An electrosensitive coating 13, preferably which is of acolor substantially different from that of the conductive layer, isdeposited on the surface of each conductive layer.

The conductive layers 12 may be of any suitable material which willadhere to the base. For example, carbon black may be mixed with anysuitable adhesive, such as gelatin, starch, cellulose ester, etc. It isdesirable to use as little binder as possible, and in general, theamount of binder may vary from to 30% of the dry weight of carbon black.

As an example of the proportions of carbon black and binder which may beutilized in forming conductive coatings for the paper, the following isgiven:

Example I 20 grams of carbon black 6 grams Methocel, or methyl cellulose(400 C. P. S.) 200 cc. water The Methocel is dissolved in cold water andthe carbon black added while stirring. The mixture is then passedthrough a colloid mill and applied to the paper base by any of thenormal coating methods, such as spraying, dipping, brushing, or knifecoating, care being taken to confine the deposition of the mixture tothe area of the recording channels on the paper, and leaving aninsulating space 14 between adjacent channels. After coating the paper,the liquid contained in the binder is evaporated off by heating or anyother suitable method. The paper is thereafter calendered to provide asmooth surface.

After the paper has been coated with the strips of conductive material,it is further processed with the electrosensitive coating, whichconsists of a white or light colored pigment and a binder. The binderutilized for the electrosensitive coating may be any one of thosementioned in connection with the conductive coating, but it ispreferable to use a binder soluble in organic solvents for theelectrosensitive coating and one soluble in water for the conductivecoating.

Zinc oxide, zinc sulphide, and barium sulphate are examples of pigmentswhich may be used satisfactorily in the electrosensitive coating.

The amount of electrosensitive coating necessary to produce asatisfactory recording paper is very small. The exact amount cannot bestated since variation in weight of the paper and variation in thicknessof the black conducting coating will cause variations. It may be said,however, that as little coating as possible should be applied; justsuflieient to cover the black conducting coating uniformly and to givethe finished surface a light gray appearance. It is necessary to applythe electrosensitive coating in such a manner as to retain the pigmenton the surface of the black coating and to guard against having thewhite pigment penetrate below the surface or between the blackconducting particles. In order that this may be done it is necessarythat the coating mixture be dried quite rapidly, since if it is driedtoo slowly, the penetration mentioned above occurs.

An example of a satisfactory electrosensitive coating is set forthbelow:

Example 11 -40 grams of zinc oxide 2.5 grams Methocel (400 C. P. S.) 100cc. water The Methocel is dissolved in cold water and the zinc a colloidmill and applied to the paper by any of the methods mentionedhereinabove. The mixture of electrosensitive coating may be applied onlyto the exposed surface of the conductive strips, or it may be applied tothe entire surface of the base material and conductive strips. In eithercase, the result is an electrosensitive paper for multi-channel directrecording in which a plurality of strips are provided on a commoncarrier and are covered with an electrosensitive coating such as wouldbe visibly aifected by the application of an electric current.

The advantage of the multi-channel recording paper of this invention canbe more fully appreciated when considered in use with the apparatusshown in Figs. 3 and 4.

Referring to Fig. 3, the string element of the galvanometer comprises aflexible conductor or string 16 which is supported at its ends by a pairof leaf springs 17 and 18. A conductive bearing sleeve 19 of a suitableferromagnetic material is disposed around and pinched to secure it tothe center of the string. The springs are arranged to provide resilientsupport for the string element along the direction of the string, andthey serve to restrain movement in all other directions, so that thedeflection of the string is not adversely affected by the end supports.

A lower magnetic pole piece 24) and a pair of spaced members 21, 22forming an upper pole piece are located on opposite sides of the stringelement, and they provide a magnetic field which is perpendicular to thelongitu dinal direction of the string. The outer end of each of theupper pole pieces is connected by a suitable yoke (not shown) to thelower pole piece to complete the magnetic circuit. A conductive guide oranvil 23 of suitable ferromagnetic material is located in the spacebetween the two upper pole pieces and spaced from them. The anvil has alower edge 24 which is perpendicular to the string and the direction ofthe magnetic field. The anvil edge is equidistant from the ends of thesleeves around the string. An electrosensitive recording paper 25 movesover the edge of the anvil so that it extends between the conductiveanvil and the sleeve on the string element of the galvanometer in theplane of motion of the string. The two upper pole pieces induce magneticpoles of opposite polarity on the anvil, so that a magnetic field isestablished in the gaps between the anvil and the two pole pieces. Themagnetic sleeve is attracted toward each of the gaps between the anviland upper pole pieces with a resultant attraction toward the anvil in adirection perpendicular to the longitudinal axis of the sleeve. Thus,the sleeve bears firmly against the surface of the paper along the linedefined by the lower edge of the anvil.

The ends of the string element are connected to receive a signal from asource 26 through a recording amplifier 27. The electric current whichfiows through the string as the result of the applied signal causes thecentral portion of the string to be deflected in accordance with themagnitude of the signals provided by the signal source.

A writing current generator 28 has one terminal grounded and anotherterminal connected through a current limiting resistor 30 to ground. Amovable tap 31 adapted to slide along resistor 30 is connected by a lead32 to the anvil. Thus, a current discharge occurs in theelectrosensitive recording paper at the intersection between the sleeveand the edge of the conductive anvil. This discharge renders the surfacecoating partially conducting, and at the same time discolors the coatingor cats it away, causing a trace to be recorded on the electrosensitiverecording paper in accordance with the movements of the string. Thebearing sleeve takes any wear which may tend to occur as the string isdeflected, and thereby greatly increases the useful life of the stringwithout unduly increasing the effective mass of the string.

Fig. 4 shows an anvil and writing set-up for a direct recordingoscillograph of the type shown in Fig. 2 which oxide added whilestirring. The mixture is passed through is adapted for two channelrecording. An anvil 40 is formed with conducting portions 41, 42 at eachend. The central portion 43 of the anvil is an electric insulator.Conducting portions 41, 42 are respectively connected by leads 44, 45 topotentiomcters 46, 47 which permit the opposite ends of the anvil to beindependently supplied adjustable amounts of current and voltage fromseparate writing current generators (not shown). Separate conductors orstrings 48, 49 are supported as described above to extendperpendicularly over the edge of the anvil, and a strip of two channeldirect recording paper, such as that shown in Fig. 1, is arranged topass between the strings and the anvils as described above.

With the arrangement of Fig. 3, each conductive portion of the anvilspans a channel on the paper and maintains the desired voltage for itsrespective channel, independent of the voltage used on the adjacentchannel.

Thus, with the paper of this invention, diflerent writing currents andvoltages may be applied to adjacent recording channels withoutinterference or burning, as occurs with presently available directrecording paper.

Fig. 5 shows an alternate form of the multi-channel recording paper ofthis invention in which a base or carriage strip 50 of paper is providedwith spaced, elongated and longitudinal portions 51 impregnated with acarbon mixture of the type described above, and a surface layer of whitepigment 52 is deposited on the conductive portions of the carriage. Thewhite pigment may be of the same type described above, and may beapplied either to the entire area of the recording paper, or limited toonly the conductive portions of the recording paper. It will be apparentthat the multi-channel paper of this invention may be formed with asmany channels as is desired or required.

Iclaim:

A recording oscillograph comprising means for producing a magneticfield, a first movable conductor, means for supporting the firstconductor in the magnetic field with the first conductor extendingtransverse to the direction of the magnetic field, a second movableconductor spaced from the first conductor, means for supporting thesecond conductor in the magnetic field with the second conductorextending transverse to the direction of the magnetic field, an anvillocated adjacent and extending transverse to the conductors,electrosensitive paper located between the anvil and the conductors, thepaper having two separate elongated and laterally spaced longitudinalstrips of conductive material on an electrically insulating base toestablish laterally spaced and electrically insulated conductivechannels, each channel having a surface coating of such character to bevisibly altered by the application of electrical marking currents, meansfor urging the conductors toward the anvil so that the paper iscontacted on one side by the anvil and on the other side by theconductors, means for imposing one voltage across the portion of thepaper adjacent the first conductor, and means for imposing anothervoltage across the portion of the paper adjacent the second conductor.

References Cited in the file of this patent UNITED STATES PATENTS2,806,756 Van Der Wcrfl Sept. 17, 1957 FOREIGN PATENTS 161,559 AustraliaMar. 1, 1955

